Preliminary Study On The Coevlution Between Phacellaria Rigidula And Its Host Plants

The viewpoint of coevolution is a new and important theoretical basis, which can be used to research the mechanism of biodiversity formation. Coevolution between plants and paints has not been studied, so we chose Phacellaria rigidula and its host plants as research material. The origin of Ph. rigidula, distribution of Ph. rigidula and its host plant, its morphology, anatomy and chemical components were discussed in this dissertation. The results were:The host plants of Phacellaria Benth. mainly belonged to Loranthaceae. Plants of Phacellaria Benth. and their hosts were mainly distributed in tropical and subtropical area. Plants of Phacellaria Benth. maybe originated in tropical area in the south of China before Tertiary. Their ancestors were parasitic on ancestors of some plants of Loranthaceae by chance during Tertiary. It took them millions of years to form a sturdy relationship between parasites and hosts.Ph. rigidula was a hemi-parasitic subshrub. In area observed, its host was mainly Taxillus caloreas var. fargesii. It mainly grew beside rivers, roads and the margin of forests and was restricted to a small patch. Dicaeum sp. maybe was Ph. rigidula's frugivorous bird and some species of Nectariniidae such as Nectarinia jugularis were pollinators of T. caloreas var. fargesii.During seedling stage, the radicle of Ph. rigidula seed burst the putamen at first. After attaching to the trunk of its host plants, the root tip of Ph. rigidula formed a haustorium that contained many mitochondrias, and then invaded the trunk of its host. It maybe involved a series of chemical signaling from its host during Ph. rigidula's germination, formation of haustorium and invasion, which was a result of coevolution between Ph. rigidula and its host. With the development of Ph. rigidula, more vessels developed in the endophyte (the portion of the haustorium that within the host) so that it absorbed more nutrients from its host. Moreover, the middle portion of the endophyte .went on invading and penetrated into the secondary xylem of the host, and there produced many new buds at two laterals of it. The stem of Ph. rigidula comprised epidermis, cortex, vascular cylinder and pith. The parenchymatous cells of cortex, pith and pith rays were filled with tannin. The vascular cylinder of the middle portion of Ph. rigidula's stem was siphonostele, and the base one was protostele.The flowers of Ph. rigidula were unisexual and most of the male and female flowers were found on different stems. There were four locules in most of the anthers and five or six locules in some anthers. There were fewer pollen grains in ananther. One pollen grain of Ph. rigidula had three germ pores. The fruit of Ph. rigidula was drupe. Its pericarp consisted of epidermis, exocarp, mesocarp (flesh) and endocarp (putamen). Colorful epidermis could attract birds to eat the fruit, endocarp which was made up of stone cells could prevent seed from being digested by digestive juice in birds' stomach, and gelatinous cell of mesocarp could make the seed stick to the trunk of its host. The characters of pericarp resulted from coevolution between Ph. rigidula and Dicaeum sp. There were four or six grooves in which contained vascular bundles on surface of putamen, and there was a cluster of hairlike substances at the apex of putamen. Compared with putamens whose flesh was removed artificially, the grooves of putamens excreted by birds were clean and smooth. Moreover, the hairlike substances were digested by Dicaeum sp. It was Dicaeum sp. that removed the inhibited factors that inhibited germination of Ph. rigidula's seeds. There were two kinds of inhibited factors, and one was inhibited substance in fresh of the fruit, and the other was hairlike substance which covered the germination pore. Fruit contained one seed, which composed of a large endosperm and a columnar embryo.The chemical components from Ph. rigidula, its hosts and their compared parasitic plants were analyzed by GC/MS and 74 compounds were found. There were both same compounds and their unique ones in parasitic plan...